Mezy can be used to post hidden messages anywhere in the world. They appear only when a follower of yours enters their geographic location, and can't be seen by anyone you haven't given permission to. These special letters can contain unlimited text, photos, and videos of up to 15 seconds in length.
Although social messaging isn't completely new in concept, Mezy seems very clever. The app is completely free, so get it from the link below if you want to start putting your print on the world map.
Mezy for iOS screenshots